1. Field of the Invention
This invention relates to a method for automatically detecting the position of the center of rotation of a rotating shaft by means of an optical flat and three sensors positioned in opposition to said optical flat.
2. Prior Art Statement
The position of the center of rotation of a rotating shaft fluctuates depending on the construction of the shaft and its bearings, speed of rotation, external forces that act on the shaft, and the like. In particular, the main spindle of a machine tool rotates while holding tools or work pieces of various shapes and weights as the machining is performed, and fluctuations directly affect the results of machining (dimensional accuracy, shape of the machined surface, etc.). Accordingly, the main spindle system must be designed such that the shaft-center fluctuations are kept to a level that is tolerable with respect to the required machining accuracy. In addition, during a precision turning operation, aligning the height of the tool tip to the position of the center of rotation with a high precision is a serious technical problem. In order to address this problem, a method for detecting the position of the center of rotation of a spindle, during unloaded rotation and during rotation while machining, at a high accuracy on the sub-micron or nanometer order must be established.
As a technique for detecting the center of rotation of a rotating shaft, the inventor of the present invention has previously proposed a method that uses a steel ball to measure the position of the center of rotation (Japanese Patent Application Public Disclosure No. 4(1992)-299209).
In this technique for measuring the position of the center of rotation using a steel ball, a steel ball is attached to the end face of the rotating shaft, and the axial displacement of the steel ball is measured during rotation of the rotating shaft. The position at which the component of the displacement signal that is synchronized with the rotation is minimized is determined to be the center of rotation.
However, in the prior art described above, the undulation components synchronized with the rotation become extremely small near the center of rotation. So, in order to find the position of the center to a high precision, high-precision guide and drive mechanisms must be used to scan a displacement sensor in two dimensions in order to find the minimum value of the undulation component synchronized with the rotation, thus requiring advanced measurement techniques. Such techniques have made the measurement device complex and expensive.
The present invention came about in light of the above, and its purpose is to provide a method and device for automatically detecting the measurable position of the center of rotation of a rotating shaft to a high precision without requiring advanced measurement techniques or complex measurement devices.